Good POP3 Server for Huge Mailboxes?

brainchill asks: "I've got about 10,000 users split between a couple of quad 550 xeon machines. The machines have 2GB of ram. The problem is that the UW POP3 server takes a huge hit in both cpu and memory utilization when a 40+MB mail spool is requested via POP3. Sometimes it's bad enough to drag the monster boxes to their knees. What other POP3 daemons do you guys have experience with and how do they perform with large mailboxes"